Research: Autonomous Navigation with Stereo and Laser Perception

Current Status

The autonomous navigation system on Nomad has undergone significant improvements
over its implementation in the Atacama Desert last year. The stereo cameras
have been equipped with auto iris lenses that significantly reduce setup
time and allow the robot to function in changing light conditions. The
change in lenses was accompanied by changes in the camera calibration procedures.
A single line laser scanner has also been added. The laser has two purposes:
to detect holes or negative height obstacles which stereo cannot see, and
to spot any other obstacles which stereo might miss. The laser has been
seamlessly integrated into the navigation system using the new goodness
map representation. The goodness map is another addition to Nomad. Each
sensor takes its data and creates a map where each cell contains a goodness
value, how good it is for the robot to be in that position, and a certainty,
the sensor's belief in the data. These maps are then passed to morphin,
which merges the maps and plans which direction to travel to maximize goodness.
This methodology allows for the easy addition of sensors, but more importantly
the goodness value may refer to something other than terrain ability such
as science value, solar availability, etc. The final major change to the
navigation system is a primitive form of error detection and recovery.
This process monitors various signals and determines when the robot is
in trouble. Currently it has two functions. It determines when the robot
is stuck too close to an object to turn away. It also monitors motor currents
and angle sensors to determine if the robot is driving on dangerous ground.
This second, referred to as blind driving, is very important in Antarctica
where the functionality of stereo and laser on ice fields is not known.
Both monitors call a backup and turn maneuver to recover from the problem.

The navigation system has been tested in Pittsburgh. The backup maneuver
has been tested, both when morphin and the blind driving modes have been
active. Morphin, with the goodness maps, has been successfully tested with
stereo as the only sensor as well as with laser as the only sensor running.

Goals

The immediate future calls for exhaustive testing in Antarctica. As a project
demonstration the autonomous navigation system will be run under various
polar conditions. Performance will be evaluated on the four major terrain
types present at Patriot Hills: blue ice field, snow, moraine (large glacial
rock deposits) and sastruggi (hardened snow hills). Of particular importance
will be the testing of the stereo vision and laser sensors on these terrain
types. The effects of and need for filters, particularly polarizing, on
the stereo cameras will be a major part of this testing, and performed
in cooperation with the French research laboratory LAAS. The navigation
system will also be capable of driving blind if the sensors should prove
ineffective.

After return from Antarctica, the navigation group will focus on three
areas of research. First, the data collected in Antarctica will be examined
thoroughly. This will provide a greater understanding of the terrain and
environmental conditions which a future meteorobot will encounter and guide
our development. Second, the method used to create a terrain map from stereo
data will be improved. The current method of fitting planes to the data
has difficulty detecting some obstacles quickly. A method employing fitting
wavelets to the data will be examined. The third area of research will
be to expand the error monitoring system to detect more faults, including
some mechanical failures.